Highly Selective Epoxidation of α-Pinene and Cinnamyl Chloride with Dry Air over Nanosized Metal Oxides

Abstract

Catalytic epoxidation of α-H-containing olefins with air over nanosized metal oxides under mild conditions has been first reported. Nanosized Co₃O₄ was considerably active for the epoxidation of α-pinene and cinnamyl chloride with air at atmospheric pressure. A substrate α-pinene conversion of 70.75 mol% with an epoxide selectivity of 87.68% was achieved at 363 K over Co₃O₄. Once Co₃O₄ was further modified with metal oxides or ammonium salts through a simple procedure consisting of ultrasonic agitation, drying and calcination, thus-prepared catalysts presented lower catalytic activity and higher epoxide selectivity than cobalt oxide itself. Over Co₃O₄ modified with surfactants, the conversion of α-pinene was somewhat reduced to 48.86–63.76 mol%, but the epoxide selectivity was increased to 92.12–94.83%. However, the composite oxide CoO _x –SnO _x (10:1) catalyzed 48.21 mol% of α-pinene conversion with 85.82% of epoxide selectivity. For the substrate cinnamyl chloride, the best result was 40.76 mol% of conversion and 87.17% of epoxide selectivity achieved by CoO _x –ZnO (5:1). It is noteworthy that the use of TBHP in small amounts initiated the reaction efficiently, and the lack of TBHP would lead to a low conversion and selectivity.

Graphical Abstract

Catalytic epoxidation of α-H-containing olefins with dry air over nanosized metal oxides under mild conditions was first reported. Co₃O₄ and Co₃O₄ modified with surfactants could catalytically convert 48.86–70.75 mol% of α-pinene, with the epoxide selectivity high up to 87.68–94.83%. The best result of cinnamyl chloride catalyzed by 5:1 CoO _x –ZnO was 40.76 mol% of conversion with 87.17% of selectivity to epoxide.